There is conventionally known a printer including a plurality of print heads as image forming units for forming images on a medium. In the printer of this type, the image forming units can form different ink images on the medium. As an example of inks, there is known a temperature-sensitive ink that changes color depending on the temperature thereof.
In the printer referred to above, it is desirable to efficiently visualize images when forming images with a temperature-sensitive ink and images with a non-temperature-sensitive ink on the medium.